Commit 8e8da023 authored Dec 04, 2011 by Linus Torvalds

x86: Fix boot failures on older AMD CPU's



People with old AMD chips are getting hung boots, because commit
bcb80e53 ("x86, microcode, AMD: Add microcode revision to
/proc/cpuinfo") moved the microcode detection too early into
"early_init_amd()".

At that point we are *so* early in the booth that the exception tables
haven't even been set up yet, so the whole

	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);

doesn't actually work: if the rdmsr does a GP fault (due to non-existant
MSR register on older CPU's), we can't fix it up yet, and the boot fails.

Fix it by simply moving the code to a slightly later point in the boot
(init_amd() instead of early_init_amd()), since the kernel itself
doesn't even really care about the microcode patchlevel at this point
(or really ever: it's made available to user space in /proc/cpuinfo, and
updated if you do a microcode load).

Reported-tested-and-bisected-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: Bob Tracy <rct@gherkin.frus.com>
Acked-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e5fd47bf

arch/x86/kernel/cpu/amd.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -442,8 +442,6 @@ static void __cpuinit bsp_init_amd(struct cpuinfo_x86 *c)

		static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
		{
		u32 dummy;

		early_init_amd_mc(c);

		/*
		@@ -473,12 +471,12 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
		set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
		}
		#endif

		rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
		}

		static void __cpuinit init_amd(struct cpuinfo_x86 *c)
		{
		u32 dummy;

		#ifdef CONFIG_SMP
		unsigned long long value;

		@@ -657,6 +655,8 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
		checking_wrmsrl(MSR_AMD64_MCx_MASK(4), mask);
		}
		}

		rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
		}

		#ifdef CONFIG_X86_32